The present invention relates to a foamable organopolysiloxane composition or, more particularly, to an organopolysiloxane composition capable of foaming and curing at room temperature and giving a silicone rubber body having a cellular foam structure of high foaming expansion and excellent uniformity so as to be useful as a material of vibration- and shock-absorbers, sound- and heat-insulators, cushions and the like.
Various methods are known in the prior art for obtaining a cellular foam of a cured silicone rubber. Japanese Patent Publication No. 45-12675 teaches a type of foamable silicone rubber compositions prepared by compounding an unfoamable room temperature-curable silicone rubber composition with a suitable blowing agent as well as reaction-foamable silicone rubber compositions in which the foamability of the composition is correlated with the mechanism of curing of the composition or the foaming gas to expand the composition is formed as a by-product of the crosslinking reaction. For example, hydrogen gas as a foaming gas is produced by the dehydrogenation reaction between a first organosilicon compound, e.g., organopolysiloxanes, having hydrogen atoms directly bonded to the silicon atoms and a second organosilicon compound, e.g., organopolysiloxanes, having hydroxy groups directly bonded to the silicon atoms as promoted by a catalytic compound which may be a quaternary ammonium salt, heavy metal carboxylate, alkali metal alkoxide and the like as is disclosed in Japanese Patent Publications Nos. 33-9297 and 44-8755. Other known catalytic compounds effective for the above mentioned dehydrogenation reaction include hydroxylamine compounds and organosilicon compounds having an aminoxy group directly bonded to the silicon atom disclosed in Japanese Patent Publication No. 45-9794 and platinum compounds disclosed in Japanese Patent Kokai No. 51-46352.
The silicone rubber foams obtained by the above described methods each have disadvantages that the foaming expansion thereof cannot be high enough in addition to the poor uniformity of the cellular structure so that, when they are used as a heat-insulating material, for example, sufficiently high heat-insulating effects can hardly be obtained. It is also proposed in Japanese Patent Kokai No. 59-196330 to admix a foamable silicone rubber composition with an organopolysiloxane resin soluble in organic solvents with an object to improve the mechanical strength of the silicone rubber foam obtained therefrom. Such a foamable rubber composition, however, is not industrially practicable and is economically disadvantageous due to the high costs.